1. Field of the Invention
The invention relates to a filter assembly for an exhaust gas purification system of an internal combustion machine. In particular, the invention relates to an internal combustion engine of a motor vehicle, in which filter plate elements are joined with one another both along their outer and inner peripheries, forming pairs of filter pockets.
2. The Prior Art
Such a filter assembly is known in the art and shown in DE 198 10 738 C. The known filter assembly is intended as a particle filter for the combustion gas purification system of an internal combustion engine for a motor vehicle. In particular, this filter assembly oxidizes the carbon black of the exhaust gas of a diesel engine. The filter assembly is formed by using porous filter plates in the form of sintered metal plate rings, which are welded together to form a filter pack comprised of filter pockets. These pockets are located in pairs on the inside and outside in an alternating manner. The filter assembly is catalytically inactive. This assembly can be combined with an oxidation catalyst and/or a catalyst for reducing the nitrogen oxide. This system enlarges the space required for installing the exhaust gas purification system.
The invention creates a filter assembly of the type specified above that permits carbon black oxidation and/or the reduction of nitrogen oxides in addition to the filtering of the carbon black particles.
The catalyzing agents are associated with the filter pockets on the outer and/or the inner sides. The catalytic functions are integrated in the filter assembly in addition to the filtration effect. In particular, there is a particle filter, so that the filter assembly represents a multifunctional device. In contrast to the prior art, the additional catalyst functions are performed without having to enlarge the volume or space required for the installation of the combustion gas purification system. This results in an extremely space-saving yet functional solution. The filter plate elements are created as dish-like elements and have a central passage, so that they have the shape of a ring.
The catalyst agents are created in the form of catalytically active foils. This represents a form of catalyst that is particularly simple and functions in a safe manner. The foils are preferably rotationally symmetrical in relation to the longitudinal axis of the filter elements, which shape is analogous to the filter plate elements. However, neither the foils nor the filter plate elements are limited to the rotation-symmetrical design, and may be shaped with corners or in some other suitable way.
In another embodiment of the invention, the foils have filter plate elements on the inwardly and outwardly disposed apexes of the filter pockets. These foils project down into the outer or inner filter pockets, in a radial manner in relation to the center axis of a filter pocket. The foils are in direct contact with the filter plate elements only within the zone of the apexes. There is nearly no rise in the combustion gas counterpressure when the filter assembly is in operation, because the foils do not represent any additional obstacle. These foils exert almost no influence on the stream of exhaust because they are located in the free space of the filter pockets.
In another embodiment of the invention, the foils have a stiffening structure. This prevents the foils from starting to flutter during the operation of the filter assembly because of the flow of exhaust gas and in particular, as a result of pressure-induced pulses caused by the flow of the combustion gas. The foils in particular have a suitable embossing for stiffening their structure.
In another embodiment of the invention, the foils are fixed in their radial alignment by the filter pockets having a supporting means. The foils are supported on part of the filter plate elements by using a suitable supporting means. In particular, the filter plate rings can have a napped structure serving as the supporting means. This napped structure supports the foils in the form of disks or disk rings over their entire surface area or in points over part of the surface.
In another embodiment of the invention, at least some of the foils have a coating that acts as an oxidation catalyst. This part of the foils is fixed on the apexes of the filter pockets located on the inner side to achieve the catalyst function on the inlet side. It is possible to oxidize carbon black contained in the combustion gas, which is preferable especially in conjunction with diesel engines. In the same manner, the foils may also be connected with the filter plate elements on the apexes located on the outer sides. These foils are then cantilevered inwards and thus mounted on the outlet side where the exhaust gas flows from the outside to the inside. The oxidation of carbon black is not promoted in this manner. However, the oxidation of HC and CO present in the combustion gas is enhanced because no deposits of carbon black or other solid particles are present on the foil on the outlet side. Thus, it is possible to achieve enhanced activity of the catalyst effect.
In yet another embodiment of the invention, at least some of the foils are actively coated with a catalyst material supporting the reduction of nitrogen oxide. In this case, the coated foils can be positioned both on the inlet and outlet sides of the stream of the combustion gas. Thus, the foils can be positioned both in the filter pockets that are open outwardly and in those that are open inwardly.
In another embodiment of the invention, metering agents such as ammonia are associated with the foils for feeding a reducing agent. In particular, feed channels are integrated in the filter assembly, serving as metering means that assure that the ammonia is injected in suitable feeding sites.
In yet another embodiment of the invention, sections of the feed channels are integrated in the filter plate elements in the form of suitably embossed structures, wherein these flow channels form one piece with the embossed structures. In this way, the metering channels are at least partially received in the filter plate elements. This is an arrangement that can be produced in a simple manner and does not require any additional structural components.